Computer information is often written to and read from a rotating recording medium. The data is recorded in concentric tracks of a magnetic disk in the form of magnetic transitions. The disks are mounted on a spindle and the information is accessed by an actuator which moves a magnetic transducer radially over the surface of the disk and aligns the transducers with the concentric tracks. The disk and spindle are mounted for rotation on a support shaft and the disks are rotated at high speeds by means of an electric motor.
Important requirements for magnetic disk files are quick access to data together with a high data rate. A key to both is high rotational speed of the disks. On average, it takes a half of a rotation of a disk for the desired data to reach the transducer after the actuator has positioned the transducer at the desired track. Thus, the higher the speed the disk rotates, the quicker the desired data can be accessed. Similarly, faster rotation of a disk causes more data to pass the transducer, increasing the data rate at the transducer.
Increased capacity is also important and has been accomplished by increasing both the data density per disk and the number of disks in a given space. The number of disks able to occupy a given space has been increased by packing the disks closer together.
The combination of higher spindle speeds and the increased number of disks has resulted in increasing the operating temperatures of high capacity, high performance disk drives. The changing temperature has a compounding effect in that increased temperature of the rotor reduces the motor efficiency and increases resistivity, thereby increasing the temperature even further due to the increased winding resistance.
Spindle motors with separate rotor assemblies and stator assemblies are commonly used for disk drive applications. The rotor generally carries a multi-polar magnet, which is mounted about a lower periphery of the rotor. The stator typically includes a radially-oriented magnet, with the polarity of areas of the magnet alternated based on the location of the multi-polar magnet in the rotor. The multi-polar magnet responds to the alternating magnetic field to rotate the rotor and disks.
In a typical assembly of a separate rotor/stator configuration, the stator is mounted to a disk drive base plate, and the rotor assembly is mounted to bearings that are, in turn, mounted about a cylindrically shaped shaft.
Various components of the rotor/stator assembly include the rotor shaft, bearings, a sleeve, a hub, the stator and stator magnet, a back iron, as well at least one disk. The increases in temperature in the disk environment may effect all components of the rotor/stator assembly. Moreover, the increases in temperature may affect the way in which the components are placed in relation to each other or interact with each other, as the various components are made of differing materials with different coefficients of expansion. Indeed, differing extents of thermal expansion in adjacent parts can distort the rotor/stator assembly as well as the disks, causing head/drive interface (HDI) problems.
Thus, it is of interest in the art to develop a rotor/stator assembly that undergoes decreased distortion at high temperatures.
An object of the present invention is to provide a hub and back iron assembly for a disk drive with decreased distortion during times of temperature change. Thus, the present invention provides a hub and back iron assembly for a disk drive, where the disk drive has a spindle and at least one disk, comprising: an annular hub having an inner side wall proximate the spindle; an outer side wall proximate the disk or disks; a top surface; and a bottom surface. The bottom surface has at least two notchesxe2x80x94inner and outer notchesxe2x80x94defined by a separating member. The inner notch accommodates a stator and the outer notch accommodates a back iron. In addition, the separating member has an outer sidewall. The hub and back iron assembly also includes a back iron disposed within the outer notch of the hub. The back iron has an inner surface proximate the spindle and coupled to the outer surface of the separating member of the hub, and an outer side wall proximate to the at least one disk and not coupled to the outer side wall of the hub. The coupling of the hub to the back iron may be accomplished by any number of means, including, but not limited to, gluing or press fitting.
In addition, the present invention provides a disk drive comprising: a base; a spindle; an annular hub having an inner side wall proximate the spindle; an outer side wall proximate the at least one disk; a top surface; and a bottom surface having inner and outer notches defined by a separating member. The inner notch accommodates a stator, the outer notch accommodates a back iron. Further, the separating member has an outer sidewall. In addition, the disk drive includes a back iron disposed within the outer notch of the hub, where the back iron has an inner surface proximate the spindle and coupled to the outer surface of the separating member of the hub, and an outer side wall proximate to the at least one disk and not coupled to the outer side wall of the hub. Further, the disk drive includes a shaft supporting at least one end of the annular hub; a fluid dynamic bearing system comprising fluid in a gap between the shaft and the sleeve and the annular hub and the sleeve; a stator; and a cover adapted to couple with the base.